Well I'm not an expert, but the ones that I've made and liked, (or seen and liked) had one or more of the following traits:
- Single color neutral sashing, especially black or white
- A single color element in the same place in all the blocks
- the scraps were sorted into general colors
- the scraps were sorted into lights and darks
- the scraps were sorted into neutrals and everything else.
I also prefer an actual pieced block as opposed to a crumb block.